This invention relates to materials used in semiconductor device fabrication for interconnects, contacts, electrodes and other conductive applications. More particularly, this invention relates to materials having desirable interdiffusion barrier properties, desirable adhesion properties, and/or low contact resistances.
Semiconductor devices, also called integrated circuits, are mass produced by fabricating hundreds of identical circuit patterns on a single semiconductor wafer. During the process, the wafer is sawed into identical dies or "chips". Although commonly referred to as semiconductor devices, the devices are fabricated from various materials, including conductors (e.g., aluminum, tungsten), non-conductors (e.g., silicon dioxide) and semiconductors (e.g., silicon). Silicon is the most commonly used semiconductor, and is used in either its single crystal or polycrystalline form. Polycrystalline silicon is often referred to as polysilicon or simply "poly". The conductivity of the silicon is adjusted by adding impurities--a process commonly referred to as "doping".
Within an integrated circuit thousands of devices (e.g., transistors, diodes, capacitors) are formed. These devices are formed by various fabrication processes, including doping processes, deposition processes, etching processes and other processes. Interconnects are formed to serve as wiring lines connecting the many devices. Contacts are formed where a device interfaces with other devices. Electrodes are formed for capacitors and other devices. Gate structures are formed for transistor devices. These interconnects, contacts, electrodes and gates are formed using conductive materials or alloys.
In forming interconnect stacks, for example, it is desirable to perform an annealing step to densify material formation and improve material properties. Often such processes include exposing the wafer to elevated temperatures, such as 500.degree. C. or higher. Exposure to these elevated temperatures may result in undesirable effects such as interdiffusion of metals, morphology changes, melting or other undesirable reactions with adjacent materials. Incorporating alloys with aluminum, for example, is used to raise the melting point and reduce electromigration effects. However, even at a low temperature, such as 100.degree. C., aluminum and silicon may react interdiffusing with each other. Such interdiffusion alters the desired device properties, resulting in product defects. Accordingly, it is known to provide a barrier layer at a silicon/metal interface. Known barrier materials for such interfaces include titanium nitride (TiN), titanium-aluminum-nitride (Ti-Al-N), titanium-tungsten (TiW), tantalum-nitride (TaN), and other materials. Such barrier layers often are 100 to 1000 .ANG. thick.
Conventional diffusion barriers such as TiN and TiW, while generally effective at lower temperatures such as room temperature, tend to fail at elevated temperatures. As many preferred semiconductor fabrication processes require elevated temperatures, these materials often prove unsatisfactory. As a result the implemented diffusion barrier often limits the types of fabrication processes that can be performed. The Ti-Al-N material as disclosed in U.S. Pat. No. 5,231,306 is an improvement over the TiN and TiW materials being more effective and being more thermally stable at elevated temperatures. Other barrier materials for preventing interdiffusion also are desirable.
Further, as more complex wiring line structures are implemented for decreasingly smaller line pitches, additional layers are being included. One difficulty in dealing with the smaller dimensions and the increasingly complex structures is promoting adhesion among the layers. Accordingly there is a need for materials useful at decreasing line pitches having improved adhesion qualities.